Determination of Nucleus Density in Semicrystalline Polymers from Nonisothermal Crystallization Curves

The present study introduces a new calculation method for obtaining nucleus density formed during nonisothermal crystallization of semicrystalline polymers. Isotactic polypropylene homopolymer (iPP) was used as a semicrystalline model polymer, and its crystalline structure was modified using highly efficient nucleating agents or different cooling rates in order to manipulate the nucleus density (N) within a wide range. The melting and crystallization characteristics were studied by calorimetry (DSC), and the nucleus density was calculated from the crystallization curves recorded under nonisothermal conditions at a constant cooling rate. The nucleus density was correlated to the optical property, in fact to the haze index of injection-molded plaques in order to qualify the calculated values of N. It was found that N increases more orders of magnitude in nucleated samples and correlates strongly to the optical properties. These observations are according to our expectations and indicate clearly the reliability of the proposed calculation approach.